PROJECT SUMMARY/ABSTRACT It is reported that 1/3rd of Americans have bedtimes after midnight, which may increase risk for cardiometabolic disease due to misalignment of the sleep period relative to the internal circadian rhythm and short sleep duration. Given the relationship between circadian alignment and disruptions in eating behaviors and insulin resistance, this study will build on our previous work by examining the neurobehavioral and dietary mechanisms that link late sleep to increased cardiometabolic risk. There is strong evidence that late sleep timing is associated with individual differences in neurobehavioral processes, such reduced ability to delay gratification and impulsivity. We propose a model in which circadian misalignment affects neurobehavioral processes and eating behaviors that increase cardiometabolic risk. In this model, exposure to short sleep duration is a moderator of these relationships. A limitation of previous research on circadian alignment is that most have been conducted as short term experiments in highly controlled laboratory settings and little attention has been paid to behavioral mechanisms. Therefore, the overarching goal of our research is to elucidate the behavioral and biological mechanisms of cardiometabolic risk among individuals with late sleep timing living under naturalistic conditions. We will to test our model of neurobehavioral vulnerability among late sleepers in a 12-month longitudinal study of 100 overweight or obese adults with late sleep timing (bedtime at 12:00 am or later). Participants will complete metabolic, sleep, diet and circadian assessments at baseline, 6 and 12 months. We will conduct neurobehavioral and eating assessments in the morning and evening to evaluate the role of time of day in neurobehavioral and eating behaviors. The aims of this study are 1. To determine the role of circadian alignment with and without short sleep duration on neurobehavioral processes, dietary behaviors and cardiometabolic risk factors, 2. To determine if time of day impacts neurobehavioral measures and dietary behaviors among overweight individuals with late sleep timing, and 3. To determine how circadian misalignment predicts changes in cardiometabolic risk over 12 months. We will test neurobehavioral measures and sleep duration as moderators of the effects of circadian misalignment in longitudinal models. Results of this study will advance knowledge of the complex relationship between sleep/circadian rhythms and cardiometabolic risk in terms of both biological and behavioral contributors, thus providing the basis for new behavioral and environmental interventions targeted to align circadian rhythms and modify neurobehavioral processes among individuals with late sleep timing.